Recent advances in portable computing have resulted in increased convenience for users of portable electronic devices. For example, mobile telephone, smart phones, computer tablets, and laptop computers allow a user to communicate while that user is mobile. That is, a user has the ability to travel freely while employing these electronic devices for communication and internet access including for navigational purposes.
In addition to portable electronic devices, many other devices use battery power. For example, battery powered automobiles and golf carts are in widespread use. Lawn mowers and other rechargeable devices such as electric toothbrushes utilize rechargeable battery power. With initiatives to reduce carbon emissions, the trend toward use of battery power may accelerate into the future.
The portable electronic devices referred to above operate on battery power which is what allows them to be mobile. That is, no power cords or other paraphernalia which might interfere with, or restrict, user movement are required. However, the user is limited by the capabilities of the battery such as power life etc. In particular, battery life may be a significant concern to a user in that it will limit the amount of time available for his or her mobility. Batteries require frequent recharging in order to maintain their power capabilities.
However, battery recharging presents challenges of its own. That is, battery chargers themselves require power cords to tether the device to the charger. Power cords gather dust and become tangled. In some cases they can be dangerous. For example, when power cords for chargers are used around water, a dangerous shock situation may develop. In addition, loose plugs or bent prongs may result in a less than successful charging cycle. Repeated use may result in wire breakage adjacent to the plug. Thus the use of electric chargers, while suited for their intended purpose, may be limited in their usefulness and convenience.
One alternative technology that is being adopted is inductive charging using wireless chargers. Wireless transmission uses a magnetic field to transfer electricity allowing compatible devices to receive power through this induced current rather than using conductive wires and cords. Inductive charging is a method by which a magnetic field transfers electricity from an external charger to a mobile device such as a phone or laptop computer without the use of standard wiring.
Inductive charging uses a charging station to send energy through an inductive coupling to an electrical device, which can then use that energy to charge batteries or run the device. Induction chargers typically use an induction coil to create an alternating electromagnetic field and create a current in the receiving device from within a charging base station. A second induction coil in the portable device takes power from the electromagnetic field and converts it back into electrical current to charge the battery. The two induction coils in proximity combine to form an electrical transformer.
The advantages of inductive charging include protected connections in that no corrosion occurs when the electronics are all enclosed and away from water or oxygen in the atmosphere. In the case of batteries used in medical implants or other embedded medical devices, inductive charging allows recharging/powering through the skin rather than having wires penetrate the skin, which would increase the risk of infection. Another advantage to inductive charging increases durability. Without the need to constantly plug and unplug the device, there is significantly less wear and tear on the socket of the device and the attaching cable.
However, there are some disadvantages to conventional inductive charging. The main disadvantages of inductive charging are its lower efficiency and increased resistive heating in comparison to direct contact charging. Inductive charging implementations using lower frequencies or older technologies may charge more slowly and generate heat within many portable electronic devices. Because of the lower efficiency, devices can take longer to charge when supplied power is equal. Inductive charging also requires drive electronics and coils in both device and charger, increasing the complexity and cost of manufacturing and therefor the cost to the user.
One additional cause for the above disadvantages and limitations of inductive charging is poor alignment of the charging coils which can cause energy losses and reduce the efficiency of the entire system. Poor efficiency reduces the charging speed of the system and requires more input power. Poor coupling can also lead to thermal issues as discussed above. Conventional solutions to the problem of misalignment of coils include increasing the number of coils into an array of coils or by including some type of coil alignment system in the inductive charging apparatus to allow the user to improve the performance of the system. Electromechanical, mechanical, or other visual alignment systems may be utilized for improved coil alignment in induction charging systems.
Inductive charging stations typically have a flat surface, often referred to as the interface surface, on top of which a user can place one or more mobile devices. As discussed above, in order for an efficient power transfer to happen, the transmitting or transceiver coil which is part of the base station must be aligned with the receiving coil, which is part of the mobile device. Two methods have been used for aligning the transmitting coil and the receiving coil in the mobile device. The first alignment method uses guided positioning where a user places the mobile device on a certain location on the base station's surface. For this purpose, the mobile device provides an alignment aid that is appropriate to its size, shape and function. This requires user effort and careful placement of the mobile device on the base station surface and limits the base station to charging mobile devices of a certain configuration.
The second alignment method allows free positioning and does not require the user to place the mobile device in direct alignment with the transmitting coil in the base station. In order to allow free positioning, a bundle of transmitting coils is included in the base station to generate a magnetic field over a larger area. This method may require the use of more energy to power additional coils. Another method to achieve free positioning provides mechanical means to move a single transmitting coil in the base station underneath the receiving coil in the mobile device. This method introduces additional mechanical complexity to the base station and requires user effort to align the coils. In effect, this method is the counterpart to the guided positioning of the mobile device.